What your ammonia reading means
Good0 ppm
Where a tank with fish should be.
Act todayAbove 0, under 1 ppm
Ammonia present: change 30 to 50 percent of the water today, feed lightly, test again tomorrow.
Act today1 ppm or more
High: change half the water now and again tomorrow, and look for the cause.
For a tank with fish. The same bands run in the test reading checker, which reads all your results together.
How much of it is toxic
The share of a total ammonia reading that is toxic NH3, and the total reading at which the toxic part reaches 0.05 ppm, the level the University of Florida gives for tissue damage. Worked out with the formula of Emerson and others (1975), the same one the checker uses.
| pH | 72 °F (22 °C) | 77 °F (25 °C) | 82 °F (28 °C) |
|---|---|---|---|
| 6.5 | 0.15% 34 ppm | 0.18% 28 ppm | 0.22% 23 ppm |
| 7 | 0.46% 11 ppm | 0.56% 8.9 ppm | 0.68% 7.3 ppm |
| 7.5 | 1.4% 3.4 ppm | 1.8% 2.8 ppm | 2.1% 2.3 ppm |
| 8 | 4.4% 1.1 ppm | 5.4% 0.93 ppm | 6.4% 0.78 ppm |
| 8.5 | 12.8% 0.39 ppm | 15.2% 0.33 ppm | 17.9% 0.28 ppm |
Where it comes from
Fish give off ammonia through their gills, and uneaten food, dead plants and any dead fish rot into more. In a settled tank, bacteria in the filter turn it into nitrite and then nitrate as fast as it appears. Ammonia shows up when that stops: a new tank, a filter cleaned too hard or switched off, too much food, too many new fish at once, or medication that harms the bacteria. Some city and well water carries ammonia too, so test your tap water once.
Toxic ammonia and ammonium
Test kits read total ammonia: two forms together. Un-ionized ammonia (NH3) is the toxic one; ammonium (NH4+) is far less harmful. The warmer and more alkaline the water, the more of the total is NH3. According to the University of Florida, toxic ammonia above 0.05 ppm damages fish tissue, and around 2 ppm sensitive fish die. The table shows what share of a reading is toxic, and the total reading at which the toxic part reaches 0.05 ppm.
Bringing it down
- Change 30 to 50 percent of the water with dechlorinated water at the same temperature. With ammonia at 1 ppm or more, change half.
- If the pH is below about 6.5, change a little water every day instead: most of the ammonia is the safer ammonium, and a big change raises the pH and turns more of it toxic (Merck Veterinary Manual, "old tank syndrome").
- Feed lightly, or not at all for a day, until it reads 0.
- Look for anything dead, and rinse filter media only in old tank water, never under the tap.
- Test ammonia and nitrite every day until both read 0.
Check all your readings together · Work out the water change
Testing it
Liquid kits and strips read total ammonia in ppm (the same as mg/L). Kits that use the Nessler method read falsely high after water conditioners that bind ammonia, and after formalin; salicylate kits are not affected, so they are the better choice if you dose a conditioner at every water change. Test pH and temperature at the same time, since you need both to judge the reading. Which test kit measures what
In a tank that is cycling
In a fishless cycle, ammonia is the food you give the bacteria: dose it to about 2 ppm and keep it there, inside the Merck Veterinary Manual’s 1 to 5 ppm; above about 4 ppm the bacteria can slow down. The cycle is done when ammonia and nitrite both read 0 within a day of dosing and nitrate is rising. The cycling guide and log